Question: 2 pencils cost $3.82. Which equation would help determine the cost of 15 pencils?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. We know the cost of 2 pencils. We want to know the cost of 15 pencils. We can write the numbers of pencils as a proportion: $\dfrac{2}{15}$ We know 2 pencils costs $3.82. We can let $x$ represent the unknown cost of 15 pencils. The proportion of these costs can be expressed as: $\dfrac{\$3.82}{x}$ The cost changes along with the number of pencils purchased, and so the two proportions are equivalent. $\dfrac{2}{15} = \dfrac{\$3.82}{x}$